| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 Section of Experimental Anesthesiology, Department of Anesthesiology and Critical Care Medicine, University of Freiburg, 79106 Freiburg, Germany; and 2 Division of Clinical Physiology, Clinic of Cardiac and Thoracic Surgery, University Hospital, 4031 Basel, Switzerland
 |
ABSTRACT |
|---|
 TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
The interrupter technique is used to determine airway and tissue resistance. Their accuracy is influenced by the technical properties of the interrupter device and the compliance of the respiratory system. We investigated the influence of valve characteristics and respiratory system compliance on the accuracy of determining airway and tissue resistance by means of a computer simulation. With decreasing compliance we found increasing errors in both airway and tissue resistance determination of up to 34 and 71%, respectively. On this basis we developed a new occlusion valve, with special emphasis on rapid closing time and tightness in the closed state to improve the accuracy of resistance determination. The newly developed occlusion device greatly improves the accuracy of airway and tissue resistance determination. We conclude that respiratory system compliance is a limiting factor for the accuracy of the interrupter technique. To apply the interrupter technique in patients with extremely low respiratory system compliances, we need sophisticated technical devices.
computer simulation; initial pressure drop; interrupter technique; respiratory system mechanics
| |
INTRODUCTION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
AIRWAY RESISTANCE (Raw) and tissue resistance (Rti) can be determined by using the interrupter technique (5). If the flow at the airway opening is suddenly interrupted and zero flow is sustained for a few seconds, the airway pressure (Paw) curve shows three different phases: rapid change in Paw being a pressure drop in inspiration and a pressure rise in expiration (phase 1); damped oscillations of a second-order system usually lasting <30 ms (phase 2) (20, 28, 29); and slow change in Paw (phase 3). The initial rapid pressure change equals the resistive pressure drop across the natural and artificial airways (2), the damped oscillations reflect ringing of the inertive components of the respiratory system (20, 29), and the slow pressure change is caused by viscoelasticity and/or mechanical inhomogeneity of the lung (2) and, in the case of spontaneous breathing, by continued muscular effort.
The point of the Paw curve that marks the transition between
phase 1 and phase
2 is called P1. The plateau pressure at the end of
phase 3 is called P2. P1 is the
essential value for the determination of Raw, and the difference P1 
P2 is required to determine Rti. However, in the presence of
pendelluft the pressure change from P1 to P2 does not reflect Rti
exclusively, because it is not possible to separate tissue rheology
from gas redistribution.
During an occlusion maneuver a certain amount of gas is still transmitted into or out of the lung. The amount of transmitted gas depends on the nonideal properties of the interrupter device, i.e., its finite closing time and its incomplete tightness. As a consequence, the pulmonary gas volume and the elastic recoil pressure change simultaneously. The amount of change in recoil pressure depends on respiratory system compliance. In effect, a long closing time and poor valve tightness, together with low respiratory system compliance, strongly influence the accuracy of the readings of the pressures P1 and P2.
The purposes of the present investigations are 1) to perform a theoretical analysis of the influence of closing time and gas tightness of an interrupter device and of respiratory system compliance on the errors in determination of Raw and Rti; 2) to screen the literature for the physical properties of the existing interrupter devices used thus far; 3) to obtain specific design criteria for a new interrupter device; 4) to develop a new interrupter device on the basis of these criteria; and 5) to investigate the technical properties of the new interrupter device in the laboratory.
| |
MATERIALS AND METHODS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Theoretical Analysis
The change in P1 and P2 because of the finite closing time and the incomplete tightness of the valve over a period of several seconds is dependent, first, on the additional volume
V passing the valve and,
second, on the patient's respiratory system compliance Crs as
described in general
|
(1) |
P is change in pressure.
The additional volume V passing the valve during its closing process
was simulated in two ways: a worst case (wc) and a realistic case (rc)
estimate. The V for the worst case was calculated as the product of
the full preocclusional flow and the simulated closing time. Depending
on the actual respiratory system compliance, the additional
postocclusional pressure change P1 due to finite closing time can be
calculated
|
(2) |
preoccl is
preocclusional flow, and
tclosing is
closing time.
Physically reasonable flow-closing profiles should generally behave like a one-quarter circle [e.g., Romero et al. (29)] or a one-half-bell-shaped function. To approximate comparable closing profiles, we assumed for the realistic case estimate a one-half-bell-shaped function, symmetrical to the point of one-half the preocclusional flow and one-half the closing time. Mathematically, the additional volume passing the valve in this case will be one-half the value of the worst case simulation. Therefore, the additional pressure change for the assumed realistic case will equal one-half the worst case estimate
|
(3) |
V passing the valve during an occlusion was
calculated as the product of leakage flow
(leak) and occlusion time
(tocclusion), here simulated to be 5 s. Depending
on respiratory system compliance, the additional slow pressure change
P2 due to leakage of the valve can also be calculated
|
(4) |
P1 and P2 on the accuracy of
estimating Raw and Rti by means of a computer simulation. We simulated
both the estimation of Raw with closing times of 5 and 15 ms and the
estimation of Rti, assuming different leakage flows over an occlusion
period of 5 s together with respiratory system compliances ranging from
80 to 10 ml/cmH2O, thus simulating normal lungs and lungs with acute respiratory distress syndrome (ARDS).
To estimate the relative errors [Raw (%) and Rti
(%)], the additional pressure changes have to be related to
reference values: we assumed Raw values of 2.5 and 4.5 cmH2O · s · l
1
and Rti values of 2.5 and 7.0 cmH2O · s · l1
for normal anesthetized paralyzed subjects and for ARDS patients, respectively, as an average taken from data presented by Eissa et al.
(11) and Tantucci et al. (33). These values do not represent individual
or standard values but have been chosen as reference values in this
study to estimate the error in the determination of Raw and Rti. Raw in
ARDS patients is independent of flow, and, in normal anesthetized
paralyzed subjects, it is reported to be flow dependent but to an
extent that is negligible for our purposes. The values for Rti were
selected at a flow rate of 1 l/s.
Equations 5 and 6 show the calculation steps for the
estimation of Raw (%)
|
(5) |
closing being the flow during the
closing process.
On the assumption that the flow during the closing process is dependent on the preocclusional flow, as it occurs in both our simulation and reality, Eq. 5 is simplified to give
|
(6) |
Equation 7 describes Rti (%)
|
(7) |
Occlusion Valve
The design of our newly developed occlusion valve is shown in Fig. 1. The occlusion valve consists of a conical valve cylinder made of Delrin (E) that is built in a valve case, with a conical valve seat made of brass (F) and a cone angle of
= 14.5°. In the "valve-open" position, the boring of the valve
cylinder that is perpendicular to its axis of rotation coincides with
the connection boring of the valve case. The inner diameter of the
boring is 15 mm. The resistance of the valve in this position is <0.3
cmH2O · s · l1
up to a flow rate of 2 l/s. To switch the occlusion valve into the
"valve-sealed" position, the valve cylinder rotates 90° by using a pneumatic high-speed drive (type PRN1-90°, Sommer,
Pforzheim, Germany) located under the valve case (not shown in Fig. 1).
The operating cycle of valve closing is subdivided into two parts: 1) the valve cylinder is lifted 0.1 mm without rotation by using a mechanical link motion (not shown) and
the pneumatic drive is accelerated, and
2) the valve cylinder is rotated
90°. Passing the 55° angle, the valve reaches the valve-closed
position, at which point the boring of the rotating
cylinder no longer has any visible contact with the connectors of the
valve case. For most applications, this position can already be seen as
gastight; any leakage is only allowed by the space between the lifted
cylinder and valve case, 0.1 mm. During the last 5° of the
cylinder's rotation, it is moved downward by the force exerted by the
compression spring (C), which also
seals the occlusion valve in the valve-sealed position. During the
operating cycle, the position of the valve cylinder is continuously
measured with an optical infrared emitter/sensor (A; type SFH 900, Siemens, Munich,
Germany). The optical measurement of the actual cylinder position is
realized by moving a special-shaped edge separating two different
infrared-reflecting materials through the visual field of the
sensor (D).
|
Further technical features are 1) guaranteed automatic reopening of the valve in case of a breakdown of the gas and/or power supply; 2) occlusions performed by means of a boring turning itself out of the gas stream, therefore not producing any artificial drafts that can cause artifacts in the pressure transducers, as is possible in the case of an occlusion plate turning inside a lumen of a tube, as described (e.g., Ref. 8); 3) computer control: possibility of single or repetitive flow-and- volume-triggered occlusions throughout the whole breath, with occlusion duration freely selectable in 2-ms steps and a delay time between trigger signal and start of cylinder rotation of 17 ms; and 4) dismantling and resterilization of all parts of the valve, with its physical characteristics remaining unaffected.
Laboratory Investigation
The experimental setup for determination of the valve characteristics includes a ventilator (Evita2, Dräger, Lübeck, Germany) to generate a constant flow rate ranging up to ±2 l/s, with the frequency set to 20 breaths/min and inspiration-to-expiration ratio set to 1:1. Gas flow rate was measured with a pneumotachograph (Fleisch no. 2, Metabo, Epalinges, Switzerland) connected to a differential pressure transducer (CPS1, Hoffrichter, Schwerin, Germany). The response of the pneumotachograph was linear over the experimental range of flow rates. The pressure drop over the valve was measured by using two relative pressure transducers (1210A, ICSensors, Milpitas, CA) at two identical pressure-measuring sites located symmetrically to the axis of rotation of the occlusion valve. The response time of the pressure sensors was 1 ms, the common mode-rejection ratio of the amplifiers was 115 dB. The flow signal, pressure signals, and output signal of the optical sensor were sampled at a rate of 250 Hz and digitized 12 bits wide (SDM863, Burr-Brown, Tucson, AZ) for subsequent numeric analysis (SparcStation 4, Sun Microsystems, Palo Alto, CA).Starting from the valve-open position, the conical cylinder of the valve was turned manually in steps of 5°. In each (static) position of the valve cylinder, three different flow rates (1, 1.5, and 2 l/s) were realized, and measurements were repeated five times. To prevent Venturi effects from affecting differential pressure measurements during the near-closed position of the valve, tubes were added on both sides of the valve.
For precise determination of closing time in relation to valve position
t(), the output voltage of the
optical sensor was measured during the closing process and stored with
a digital storage oscilloscope at a sample frequency of 20 kHz (Nicolet 490, Madison, WI). In addition, the output voltage of the optical sensor was measured while the cylinder of the valve was turned manually
in steps of 2°. The function
t() was finally calculated by using
a second-order polynomial least squares fit.
To quantify the leakage of the valve in the valve-closed (>55°) and valve-sealed positions (90°), the ventilator (Evita2) was set in the continuous positive Paw mode, which ranged from 5 to 20 cmH2O, while the whole valve was submerged underwater to enable the capture of the smallest volumes of gas leakage. The time during which a certain leakage volume passed the valve was measured, and the leakage flow was determined as the quotient of leakage volume and time. The values were corrected for the hydrostatic pressure.
| |
RESULTS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Theoretical Analysis
Figure 2 shows the relative error in the estimation of Raw obtained in the first simulation. The diagram shows that the error in the estimation of Raw 1) increases with increasing closing time and 2) increases with decreasing respiratory system compliance. In particular, for a very low compliance, which simulates severe ARDS, the error increases to 17 and 34%, assuming a closing time of an occlusion device of 15 ms and realistic or worst case conditions, respectively. Even for very low closing times of 5 ms, the errors in the presence of extremely low respiratory system compliance are still as high as 6 and 12% for realistic and worst case estimates, respectively.
|
Figure 3 shows the relative error in the
estimation of Rti obtained in the second simulation. The diagram also
shows that the error in the estimation of Rti
1) increases with increasing leakage
flow and 2) increases with
decreasing respiratory system compliance. For a very low compliance and
a leakage flow through the occlusion device of 10 ml/s over a period of
5 s, the error increases to 71%. With respiratory system compliances
ranging from 80 to 20 ml/cmH2O,
only the use of extremely tight valves with leakage flows of ~0.5
ml/s produced errors that are generally <2%. For a very low
compliance of 10 ml/cmH2O, the
error is still 3.6%.
|
Development of a New Occlusion Valve
Conductance during the closing cycle.
Figure 4A
shows the relationship between the conductance of our occlusion valve
and the valve angle measured under static conditions. As the diagram
shows, conductance is first markedly decreased, starting at a closing
angle of 10°, resulting in a reduced closing time and an increase
in trigger delay (between software command and actual begin of
closing).
|
|
(8) |
|
(9) |
0.05 (t 
2 ms), the root
mean square error is 0.08 l · s1 · cmH2O1.
Leakage of the valve.
Table 1 gives the leakage in the closed
position (55-90°), which is <6 ml/s at a pressure difference
over the closed valve of 10 cmH2O.
The valve remains in this status for ~4.5 ms, so that the leakage
volume during this time would be <0.03 ml. Therefore, the valve is
effectively closed at a valve angle of 55°. Table 1 shows that the
leakage in the sealed position (90°), with pressure differences
over the sealed valve ranging from 5 to 20 cmH2O, is <0.6 ml/s in all
cases.
|
| |
DISCUSSION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
In the present study, we investigated the influence of respiratory system compliance and of the nonideal technical properties of an occlusion device on the accuracy of Raw and Rti determination. During an occlusion maneuver, a certain amount of gas is still transmitted through the occlusion device. The reasons for this gas transmission are mainly the finite closing time of the occlusion device but also its incomplete tightness in the closed state. As a consequence, the pulmonary gas volume changes, thereby inducing a concomitant change in alveolar pressure that is dependent on respiratory system compliance.
Especially in the presence of severely reduced respiratory system compliance, as seen in ARDS, the change in the elastic recoil pressure will be particularly high, and hence the errors in estimating Raw and Rti are large. However, for this particular group of patients a precise determination of respiratory system mechanics is urgently desired by clinicians at the bedside. For this reason, we developed a new occlusion device based on the theoretical evaluation of errors, eliminating most of the technical problems of the interrupter technique.
Theoretical Analysis
In the first computer simulation (Fig. 2), we found that the relative errors in Raw depended considerably on respiratory system compliance. With decreasing compliance the relative errors can become as large as 34%, caused by errors in the reading of P1.The flow through the occlusion device during its closing process is bidirectional: into the lungs in inspiration (assuming the ventilator does not stop gas delivery within 15 ms due to pressure limits) and out of the lungs in expiration, both resulting in a smaller initial pressure drop and consequently an underestimation of Raw (4).
P1 determination. Several methods for the correction of the errors in the determination of P1 have been described. To our knowledge Bates et al. (4) first investigated the influence of valve closing time on the estimation of respiratory system resistance. With their backextrapolation method, the authors could reduce the error in the estimation of Raw from 7 to 1-2%. However, because of the additional volume passing the valve during its closing process, the whole pressure-time curve is shifted to higher or lower values during inspiratory or expiratory occlusion maneuvers. The backextrapolation method would then only yield an under- or overestimated value for P1 (22).
A second correction method offers the use of the Fourier transform: on the assumption that the respiratory system is linear, the pressure signal can be expressed as the convolution of the flow signal with the impulse response of the respiratory system. The pressure signal can then be corrected as described by Romero et al. (29). However, this method requires knowledge of the flow profile during the closing process of the occlusion device. Kochi et al. (22) first took account of the compliance of the respiratory system by mathematically correcting their resistance values. To use their correction method, however, one has to know the compliance of the respiratory system as well as the volume passing the valve during its closing process.P2 determination. To our knowledge, the influence of the incomplete valve tightness on the accuracy of estimating Rti has not been investigated previously.
The second computer simulation revealed errors in the estimation of Rti of up to 71%, in the presence of a leakage flow of 10 ml/s and 5-s occlusion time and considerably decreased respiratory system compliance. The demand for a very tight valve becomes obvious: even with a leakage flow of only 0.5 ml/s, the relative errors in the determination of Rti rise to 3.6%, assuming a compliance of 10 ml/cmH2O. By using a correction method similar to that of Kochi et al. (22), these errors can be corrected
|
(10) |
Vocclusion is the change in occlusion volume. However,
again, there are the same problems as mentioned above: determination of
respiratory system compliance and determination of minimal leakage
flows with conventional flow-measuring devices.
Generally, neither the flow during the closing process nor the leakage
flow during an occlusion maneuver can be captured faithfully (29). The
flow occurring during the closing process changes too quickly to be
reliably measured, and the leakage flow during an occlusion is usually
too small to be reliably measured with the same flow-measuring device
used for general flow measurements in humans. Consequently, the
transmitted gas volume cannot be measured, and there is no easy way to
estimate and to correct for the errors in the readings of P1 and P2 by
using the method as described by Kochi et al. (22) and
Eq. 10. The only way in which this
would be possible is by analyzing the physical properties of an
interrupter device and therefore knowing the closing functions and
leakage flows under certain conditions. However, even then the
correction possibilities are limited: with low respiratory system
compliance the errors become very large, and to correct for errors of
50% or more is not reasonable. Therefore, the demand for a rapidly
closing and sufficiently tight occlusion valve remains.
There is no influence of the finite closing time on the estimation of
Rti, as reported by Bates et al. (4) and Sly and Bates (31). The
problem, however, is the incorrect determination of P1 due either to
the pressure oscillations, which occur immediately after occlusion, or
to erroneous backextrapolation of the pressure signal. This results in
an erroneous Raw as well as a false difference P2 P1;
therefore, Rti would also be incorrect. The precise determination of P1
is the most important point in using the interrupter technique to
determine respiratory system resistances. One should put special emphasis on its precise determination as both Raw and Rti are dependent
on the correct value of P1.
Neither simulation includes the case of normal respiratory system
compliance and extremely increased resistance as seen in patients with
chronic obstructive pulmonary disease. However, because of the
increased time constant and the mechanical inhomogeneity, the use of
the interrupter technique in patients with severe chronic obstructive
pulmonary disease is controversial in any case (28).
Existing Occlusion Devices
Since the introduction of the airway occlusion technique by von Neergaard and Wirz in 1927 (24), many research groups have used this technique to determine respiratory system resistance in animals (17, 22), in excised isolated lungs (12), in patients during controlled mechanical ventilation (18), and in intubated spontaneously breathing patients during weaning from mechanical ventilation (27).Many different types of interrupter devices have been used so far (see
Table 2), and surely many of them have
fulfilled the operating requirements. However, the physical properties
of most devices were not described in detail. Therefore, for most
devices it is unknown whether they can be used for fast short-term
occlusions as well as for rapidly closing long-term occlusions. There
was always the compromise between rapid closing on the one hand and long-term tightness on the other.
|
On the basis of these considerations and the results of our computer simulations, an occlusion device has to meet the following criteria: 1) very short valve-closing time; 2) strong tightness over a period of several seconds in the closed position; 3) minimal resistance in the open position, especially for use in spontaneously breathing patients; 4) small dead space, especially for the use in pediatrics; 5) no vibrations or "turning drafts" because of the closing process to avoid additional artifacts; 6) integrated measurement of the valve position to determine P1 on the time axis and to establish a closing function; 7) maintenance of its characteristics under adverse day-to-day conditions and under continuous use; and 8) minimal effect because of real-world difficulties, such as moisture accumulation or wear caused by repetitive cycling.
Unfortunately, the two most important demands, a fast closing time and tightness, are contradictory. Rapid closure in the physical sense usually means little friction between closing element and case, and little friction usually stands for poor tightness. This may be the reason that hardly any data are available in the literature (see Table 2) for both the closing time and the leakage of one valve.
New Occlusion Valve
As far as we know, there are no commercially available occlusion valves that satisfy all the necessary conditions mentioned above. Therefore, we have designed a new type of occlusion valve whereby valve closure and valve sealing are two physically separate processes. We constructed a valve that effectively closes within 10 ms and is pressure tight, with a minimal leakage flow in the sealed position of <0.6 ml/s at a pressure difference over the valve of up to 20 cmH2O.To estimate the additional volume passing the valve during its closing
process, the flow has to be integrated to volume. We assumed the flow
to be similar to the conductance profile, changing from
0 to zero
according to Eq. 9
|
(11) |
0 is the
flow in the open position.
With (t) = o = 1 l/s
(t < 2 ms) and
b = c = 0.05 (t 2 ms),
the additional volume passing our valve during its 10-ms closing
process is as small as 3.4 ml.
Where in the simulation is our new interrupter device positioned? An additional volume passing the valve of ~3.4 ml would place our valve between the worst case and realistic case simulations for a valve closing time of 5 ms at a preocclusional flow of 1 l/s (worst case: 5 ms · 1 l/s = 5 ml; realistic case: 2.5 ml; see Fig. 2). The error in the estimation of Raw without any corrections for closing time would be generally <3%; only in patients with low respiratory system compliance values of 20 or 10 ml/cmH2O would the error rise to 5 and 10%, respectively. However, these errors still appear to be very high but can finally be corrected further by using one of the correction methods for valve closing time described previously. A comparable error estimation in relation to respiratory system compliance has not been done by other authors so far, except by Kochi et al. (22) in cats.
With a leakage flow of <0.6 ml/s, our valve is placed close to the simulated leakage flow line of 0.5 ml/s (Fig. 3). The relative error in the estimation of Rti would be ~2%. However, in the presence of very low respiratory system compliance, the relative error would rise to ~4%.
These results show that our new valve fulfills both requirements: rapid closing and sufficient tightness in the closed position.
In conclusion, the nonideal technical properties of an occlusion device in combination with reduced respiratory system compliance considerably influence the accuracy in determining Raw and Rti by using the interrupter technique. The existing devices that have been used until now were more or less suitable for determining either Raw or Rti. On the basis of the very limited technical descriptions in the literature, hardly any of the existing devices are suitable for determining both values with sufficient accuracy.
Our newly developed occlusion valve circumvents these problems and can be considered a universal tool for using the interrupter technique, with acceptable errors in the determination of Raw and Rti, in patients with a variety of clinical conditions.
This work may be a further step toward a standardized use of the interrupter technique as proposed by Carter et al. (6).
| |
ACKNOWLEDGEMENTS |
|---|
The authors are indebted to Dr. Jason H. T. Bates (Montreal), Dr. Heike L. Pahl (Freiburg), and Dr. Kai Rehder (Rochester) for most helpful, stimulating, and critical discussions and to Björn Lorenz and Matthias Schneider for technical assistance.
| |
FOOTNOTES |
|---|
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: V. Kessler, Sektion Experimentelle Anästhesiologie, Anästhesiologische Universitätsklinik, Universität Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany (E-mail: kessler{at}ana1.ukl.uni-freiburg.de).
Received 26 October 1998; accepted in final form 8 June 1999.
| |
REFERENCES |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
1.
Altena, R., Van,
and
F. Gimeno.
Respiratory resistance measured by flow-interruption in a normal population.
Respiration
61:
249-254,
1994[Medline].
2.
Bates, J. H. T.,
P. Baconnier,
and
J. Milic-Emili.
A theoretical analysis of the interrupter technique for measuring respiratory mechanics.
J. Appl. Physiol.
64:
2204-2214,
1988
3.
Bates, J. H. T.,
K. A. Brown,
and
T. Kochi.
Respiratory mechanics in the normal dog determined by expiratory flow interruption.
J. Appl. Physiol.
67:
2276-2285,
1989
4.
Bates, J. H. T.,
I. W. Hunter,
P. D. Sly,
S. Okubo,
S. Filialtrault,
and
J. Milic-Emili.
Effect of valve closure time on determination of respiratory resistance by flow interruption.
Med. Biol. Eng. Comput.
25:
136-140,
1987[Medline].
5.
Bates, J. H. T.,
and
J. Milic-Emili.
The flow interruption technique for measuring respiratory resistance.
J. Crit. Care
6:
227-238,
1991.
6.
Carter, E. R.
It is time to consider standardizing the interrupter technique.
Eur. Respir. J.
10:
1428-1429,
1997[Medline].
7.
Carter, E. R.,
A. A. Stecenko,
B. H. Pollock,
and
M. J. Jaeger.
Evaluation of the interrupter technique for the use of assessing airway obstruction in children.
Pediatr. Pulmonol.
17:
211-217,
1994[Medline].
8.
Chowienczyk, P. J.,
C. P. Lawson,
S. Lane,
R. Johnson,
N. Wilson,
M. Silverman,
and
G. M. Cochrane.
A flow interruption device for measurement of airway resistance.
Eur. Respir. J.
4:
623-628,
1991[Abstract].
9.
Clarke, J. R.,
M. J. Jaeger,
J. L. Zumrick,
R. O'Bryan,
and
W. H. Spaur.
Respiratory resistance from 1 to 46 ATA measured with the interrupter technique.
J. Appl. Physiol.
52:
549-555,
1982
10.
Clements, J. A.,
J. T. Sharp,
R. P. Johnson,
and
J. O. Elam.
Estimation of pulmonary resistance by repetitive interruption of airflow.
J. Clin. Invest.
38:
1262-1270,
1959.
11.
Eissa, N. T.,
V. M. Ranieri,
C. Corbeil,
M. Chassé,
F. M. Robatto,
J. Braidy,
and
J. Milic-Emili.
Analysis of behavior of the respiratory system in ARDS patients: effects of flow, volume and time.
J. Appl. Physiol.
70:
2719-2729,
1991
12.
Fichter, J.,
W. Wierich,
and
W. Hartung.
Resistance measurement in normal and obstructed excised human lungs by means of the interrupter method.
Respiration
56:
34-42,
1989[Medline].
13.
Fletcher, M. E.,
C. A. Dezateux,
and
J. Stocks.
Respiratory compliance in infants
a preliminary evaluation of the multiple interrupter technique.
Pediatr. Pulmonol.
14:
118-125,
1992[Medline].
14.
Freezer, N. J.,
C. J. Lanteri,
and
P. D. Sly.
Effect of pulmonary blood flow on measurements of respiratory mechanics using the interrupter technique.
J. Appl. Physiol.
74:
1083-1088,
1993
15.
Frey, U.,
and
R. Kraemer.
Interrelationship between postocclusional oscillatory pressure transients and standard lung function in healthy and asthmatic children.
Pediatr. Pulmonol.
19:
379-388,
1995[Medline].
16.
Frey, U.,
B. Suki,
R. Kraemer,
and
A. C. Jackson.
Human respiratory input impedance between 32 and 800 Hz, measured by interrupter technique and forced oscillations.
J. Appl. Physiol.
82:
1018-1023,
1997
17.
Gottfried, S. B.,
A. Rossi,
L. Calverley,
L. Zocchi,
and
J. Milic-Emili.
Interrupter technique for measurement of respiratory mechanics in anesthetized cats.
J. Appl. Physiol.
56:
681-690,
1984
18.
Gottfried, S. B.,
A. Rossi,
B. D. Higgs,
P. M. A. Calverley,
L. Zocchi,
C. Bozic,
and
J. Milic-Emili.
Noninvasive determination of respiratory system mechanics during mechanical ventilation for acute respiratory failure.
Am. Rev. Respir. Dis.
131:
414-420,
1985[Medline].
19.
Hultzsch, W.,
and
G. Lipowsky.
Intrapulmonale Druckmessungen bei Hochfrequenzbeatmung extrem kleiner Frühgeborener.
Monatsschr. Kinderheilkd.
140:
476-482,
1992[Medline].
20.
Jackson, A. C.,
H. T. Milhorn,
and
J. R. Norman.
A reevaluation of the interrupter technique for airway resistance measurement.
J. Appl. Physiol.
36:
264-268,
1974
21.
Knudson, R. J.,
J. Mead,
and
D. E. Knudson.
Contribution of airway collapse to supramaximal expiratory flows.
J. Appl. Physiol.
36:
653-667,
1974
22.
Kochi, T.,
S. Okubo,
W. A. Zin,
and
J. Milic-Emili.
Flow and volume dependence of pulmonary mechanics in anesthetized cats.
J. Appl. Physiol.
64:
441-450,
1988
23.
Liistro, G.,
D. Stanescu,
D. Rodenstein,
and
C. Veriter.
Reassessment of the interruption technique for measuring flow resistance in humans.
J. Appl. Physiol.
67:
933-937,
1989
24.
Neergaard, K., Von,
and
K. Wirz.
Die Messung der Strömungswiderstände in den Atemwegen des Menschen, insbesondere bei Asthma und Emphysem.
Z. Klin. Med.
105:
51-82,
1927.
25.
Ohya, N.,
J. Huang,
T. Fukunaga,
and
H. Toga.
Mouth pressure curve on abrupt interruption of airflow during forced expiration.
J. Appl. Physiol.
66:
509-517,
1989
26.
Oswald-Mammosser, M.,
C. Llerena,
J. P. Speich,
L. Donato,
and
J. Lonsdorfer.
Measurements of respiratory system resistance by the interrupter technique in healthy and asthmatic children.
Pediatr. Pulmonol.
24:
78-85,
1997[Medline].
27.
Pesenti, A.,
P. Pelosi,
G. Foti,
L. D'Andrea,
and
N. Rossi.
An interrupter technique for measuring respiratory mechanics and the pressure generated by respiratory muscles during partial ventilatory support.
Chest
102:
918-923,
1992
28.
Phagoo, S. B.,
R. A. Watson,
N. B. Pride,
and
M. Silverman.
Accuracy and sensitivity of the interrupter technique for measuring the response to bronchial challenge in normal subjects.
Eur. Respir. J.
6:
996-1003,
1993[Abstract].
29.
Romero, P. V.,
J. Sato,
F. Shardonofsky,
and
J. H. T. Bates.
High-frequency characteristics of respiratory mechanics determined by flow interruption.
J. Appl. Physiol.
69:
1682-1688,
1990
30.
Schlesinger, R. B.,
A. V. Zeccardi,
and
J. Monahan.
An interrupter method for measurement of airway resistance in small animals.
J. Appl. Physiol.
48:
1092-1095,
1980
31.
Sly, P. D.,
and
J. H. T. Bates.
Computer analysis of physical factors affecting the use of the interrupter technique in infants.
Pediatr. Pulmonol.
4:
219-224,
1988[Medline].
32.
Smith, P. G.,
A. Falahat,
and
W. A. Carlo.
Measurement of interrupter resistance in rabbits exposed to methacholine aerosols.
J. Appl. Physiol.
72:
2454-2457,
1992
33.
Tantucci, C.,
C. Corbeil,
M. Chassé,
F. M. Robatto,
S. Nava,
J. Braidy,
N. Matar,
and
J. Milic-Emili.
Flow and volume dependence of respiratory system flow resistance in patients with adult respiratory distress syndrome.
Am. Rev. Respir. Dis.
145:
355-360,
1992[Medline].
34.
Vooren, P. H.,
and
B. C. Van Zomeren.
Reference values of total respiratory resistance, determined with the "opening" interruption technique.
Eur. Respir. J.
2:
966-971,
1989[Abstract].
This article has been cited by other articles:
|
|
 |
|
  N. Beydon, S. D. Davis, E. Lombardi, J. L. Allen, H. G. M. Arets, P. Aurora, H. Bisgaard, G. M. Davis, F. M. Ducharme, H. Eigen, et al. An Official American Thoracic Society/European Respiratory Society Statement: Pulmonary Function Testing in Preschool Children Am. J. Respir. Crit. Care Med., June 15, 2007; 175(12): 1304 - 1345. [Full Text] [PDF]
|
|
|
|
 |
|
 G. Mols, V. Kessler, A. Benzing, M. Lichtwarck-Aschoff, K. Geiger, and J. Guttmann Is pulmonary resistance constant, within the range of tidal volume ventilation, in patients with ARDS? Br. J. Anaesth., February 1, 2001; 86(2): 176 - 182. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Q. LU, A. CAPDEROU, P. CLUZEL, E. MOURGEON, L. ABDENNOUR, J.-D. LAW-KOUNE, C. STRAUS, P. GRENIER, M. ZELTER, and J.-J. ROUBY A Computed Tomographic Scan Assessment of Endotracheal Suctioning-Induced Bronchoconstriction in Ventilated Sheep Am. J. Respir. Crit. Care Med., November 1, 2000; 162(5): 1898 - 1904. [Abstract] [Full Text]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
